1. Field of the Invention
The present invention relates to a receiving/transmitting apparatus for radiating a predetermined signal and receiving a signal arriving as a response to the radiated signal and a radar equipment in which the receiving/transmitting apparatus is installed.
2. Description of the Related Art
In recent years, a technique for realizing sophisticated signal processing at a high speed and at a low price has been established and such signal processing has been widely applied to various electronic apparatuses and systems.
This signal processing technique has been increasingly applied to, for example, radio application equipments and navigation aids such as radar equipments, among the above-mentioned electronic apparatuses, as an indispensable element technique for achieving high performance and reliability under desirable environment conditions or for heightening added values as well as for realizing adaptability to severe demands for price reduction, downsizing, lightening, energy saving, and others.
FIG. 8 is a diagram showing a first structure example of a receiving/transmitting part of a radar equipment to which the signal processing technique is applied.
In FIG. 8, one output of a COHO oscillator 51 is connected to an input of a mixer 52, and to a local-frequency input of the mixer 52, one output of an STALO oscillator 53 is connected. An output of the mixer 52 is connected to a first aperture of a circulator 56 via a pulse modulator (SW) 54 and a power amplifier 55 which are connected in cascade. To a second aperture of the circulator 56, a feeding point of an antenna 57 is connected, and a third aperture of the circulator 56 is connected to an input of the mixer 58. To a local-frequency input of the mixer 58, the other output of the STALO oscillator 53 is connected. An output of the mixer 58 is connected to an input of a quadrature demodulator 59. To a carrier input of the quadrature demodulator 59, the other output of the COHO oscillator 51 is connected and an output of the quadrature demodulator 59 is connected to an input of a not-shown signal processing part.
In the radar equipment as structured above (hereinafter referred to as a xe2x80x98first conventional examplexe2x80x99), the COHO oscillator 51 constantly generates a reference signal with a predetermined frequency fc. The STALO oscillator 53 also generates a local-frequency signal with a predetermined frequency fs constantly.
The mixer 52 generates a transmitting signal with a frequency ft (=fc+fs) equal to the sum of the frequencies of the reference signal and the local-frequency signal. The pulse modulator 54 performs on-off keying of the transmitting signal at a predetermined duty factor to generate a transmission wave and radiates the transmission wave via the power amplifier 55, the circulator 56, and the antenna 57.
A reflected wave reaching the antenna 57 from a target in response to the transmission wave is fed to the mixer 58 via the circulator 56.
The mixer 58 converts the reflected wave to an intermediate frequency signal with a frequency equal to a difference fr (=ftxe2x88x92fs=fc) between a frequency of the reflected wave and the frequency of the local-frequency signal which is generated by the STALO oscillator 53.
The quadrature demodulator 59 quadrature-demodulates the intermediate frequency signal according to the reference signal which is given by the COHO oscillator 51 to generate demodulation signals I, Q which are in quadrature.
The aforesaid signal processing part performs predetermined signal processing for the demodulation signals I, Q to realize, for example, improvement in SN ratio, MTI, and others.
Incidentally, in the process of the signal processing, as long as the COHO oscillator 51 and the STALO oscillator 53 constantly generate the aforesaid reference signal and the local-frequency signal respectively with desirable precision, phases of components of the reflected wave, which arrives from the target located in a fixed relative distance, relative to a phase of the reference signal do not vary (hereinafter, to satisfy this condition is simply referred to as xe2x80x98coherencyxe2x80x99), and therefore, the improvement in the SN ratio and so on based on integrating processing and the like is achieved with high reliability.
FIG. 9 is a diagram showing a second structure example of a receiving/transmitting part of a radar equipment to which the signal processing technique is applied.
The radar equipment shown in FIG. 9 is characterized in that:
a variable frequency oscillator 61 is provided to substitute for the COHO oscillator 51;
a coupler 62 is provided to substitute for the mixer 52;
neither the pulse modulator 54 nor the STALO oscillator 53 is provided; and
the power amplifier 55 has a control terminal to which a later-described control signal is given together with a control input of the variable frequency oscillator 61.
Note that the same numerals and symbols are used to designate elements having the same functions as those of the elements shown in FIG. 8 and explanations thereof are omitted here.
In the radar equipment as structured above (hereinafter referred to as a xe2x80x98second conventional examplexe2x80x99), the variable frequency oscillator 61 alternately generates two signals having the same frequencies as those of the aforesaid transmitting signal and the local-frequency signal respectively (hereinafter referred to as a xe2x80x98transmission wave signalxe2x80x99 and a xe2x80x98receiving local-frequency signalxe2x80x99 respectively) according to logical values of a binary control signal which gives the aforesaid duty factor.
Note that periods during which the transmission wave signal and the receiving local-frequency signal are generated by the variable frequency oscillator 61 are hereinafter referred to as xe2x80x98transmitting timexe2x80x99 and xe2x80x98receiving timexe2x80x99 respectively for simplification.
The coupler 62 processes the following based on a difference between the frequency of the transmission wave signal and the frequency of the receiving local-frequency signal which are thus generated by the variable frequency oscillator 61.
to send the transmission wave signal to the power amplifier 55 but prevent its feeding to the mixer 58
to send the receiving local-frequency signal to the mixer 58 but prevent its feeding to the power amplifier 55
The power amplifier 55 amplifies the transmission wave signal to be fed via the coupler 62 within the transmitting time which is given as the logical value of the aforesaid control signal and radiates the transmission wave signal as a transmission wave via the circulator 56 and the antenna 57.
The mixer 58 generates an intermediate frequency signal with a frequency equal to a difference between the frequency of the reflected wave, which reaches the antenna 57 during the above receiving time and is fed thereto via the circulator 56, and the frequency of the receiving local-frequency signal, which is fed thereto via the coupler 62 during the receiving time, and feeds the intermediate frequency signal to the quadrature demodulator 59.
In other words, the variable frequency oscillator 61 is commonly used for generating the receiving local-frequency signal during the receiving time and generating the transmission wave signal during the transmitting time while securing isolation between a transmitting part and a receiving part.
Therefore, in the second conventional example, where neither the pulse modulator 54 nor the STALO oscillator 53 shown in FIG. 8 is provided, the hardware structure is simplified compared with that in the first conventional example.
Incidentally, the same processing as in the first conventional example is performed by the quadrature demodulator 59 and the signal processing part which is provided on a subsequent stage of the quadrature demodulator 59 and therefore, explanations thereof are omitted here.
Note that the reference signal and the local-frequency signal are constantly generated in the above-described first conventional example.
Consequently, though the aforesaid coherence is secured, it is necessary to provide some hardware such as electromagnetic shielding and others for preventing cross-talk of the reference signal (given to the mixer 52 also during the period in which the reflected wave is to be received), the transmission wave signal, and the transmission wave to the mixer 58 and its subsequent stages from the mixer 52 via the pulse modulator 54 and the power amplifier 55, in order to avoid mis-detection which may possibly be caused particularly because the transmission wave and the reflected wave have the same frequency.
Therefore, the first conventional example requires an enlarged hardware scale and does not satisfy restrictions on cost, mountability, and others.
Meanwhile, in the second conventional example, since the frequencies of the aforesaid receiving local-frequency signal and the transmission wave signal are set at different values from each other, no electromagnetic shielding mentioned above is required but the variable frequency oscillator 61 oscillates the receiving local-frequency signal and the transmission wave signal alternately during the transmitting time and the receiving time.
Consequently, in the second conventional example, a phase difference between the transmission wave signal and the receiving local-frequency signal fluctuates in every new transmitting time and receiving time, as shown in FIG. 10(a) so that the coherency is not secured and the components of the reflected wave are integrated by the signal processing part, for example, as shown in FIG. 10(b).
As a result, the possibility that precision in the signal processing is degraded and desirable improvement in the SN ratio and desirable performance are not achieved in the signal processing process is high compared with the first conventional example.
It is an object of the present invention to provide a receiving/transmitting apparatus and a radar equipment in which coherency is achieved with high reliability, without causing any great enlargement in hardware scale.
It is another object of the present invention to separate the components of a reception wave at its every phase and to improve precision in signal processing which is performed for the components, without causing any great enlargement in hardware scale.
It is still another object of the present invention to simplify hardware structure.
It is yet another object of the present invention to stably achieve a desirable function and performance.
It is yet another object of the present invention to efficiently and highly reliably measure all or a part of the characteristic, shape, size, and material of a medium through which an emission wave a nd a reception wave propagate, even when the reception wave is very weak.
It is yet another object of the present invention to realize flexible adaptability of the structure t o the frequencies of an emission wave a nd a reception wave.
It is yet another object of the present invention to stably realize highly precise signal processing without any means for setting loose coupling or shielding coupling with means for generating a local-frequency signal which is used for receiving a reception wave.
It is yet another object of the present invention to stably achieve highly precise signal processing.
It is yet another object of the present invention to realize structure simplification as well as price reduction.
It is yet another object of the present invention to detect a reception wave efficiently and highly reliably even when the reception wave is very weak, as long as the characteristic of a propagation path of an emission wave and a reception wave, a time required for a target to respond, and the characteristic of the target do not vary.
It is yet another object of the present invention to measure all or a part of the characteristic of a medium interposed between the radar equipment and its target, a relative distance and a relative position to the target, and a relative speed and a size of the target, even when the reception wave is very weak.
It is yet another object of the present invention to highly maintain reliability and precision in identifying a target.
It is yet another object of the present invention to realize with high reliability improvement in performance and reliability as well as price reduction, downsizing, and running cost reduction in apparatuses and systems to which the present invention is applied.
The above objects are achieved by a receiving/transmitting apparatus which alternately generates the first signal and the second signal whose frequencies are different from each other and whose phases have different fixed initial values from each other, radiates an emission wave generated based on the first signal, and heterodyne-detects, according to the second signal, a reception wave received as a response to the emission wave to separate components of the reception wave at its every phase relative to the first signal or the second signal.
In the receiving/transmitting apparatus ascribed above, an initial value of a phase of the radiated emission wave is maintained at a fixed value every time the emission wave is transmitted, even though a signal generating section is used for both the generation of the emission wave and the heterodyne detection of the aforesaid reception wave.
The above objects are also achieved by a receiving/transmitting apparatus which radiates the first signal as an emission wave.
In the receiving/transmitting apparatus as described above, an initial value of a phase of the radiated emission wave is maintained at a fixed value every time the emission wave is transmitted, even though a signal generating section is used for both the generation of the emission wave and the heterodyne detection of the aforesaid reception wave.
The above objects are also achieved by a receiving/transmitting apparatus which alternately performs frequency synthesis according to two different synthetic ratios, in response to a reference signal with a fixed frequency, to generate the first signal and the second signal.
In the receiving/transmitting apparatus as described above, the first signal used for generating an emission wave or corresponding to the emission wave and the second signal used for receiving a reception wave are generated by performing the frequency synthesis according to the different synthetic ratios on the reference signals having a common frequency.
The above objects are also achieved by a receiving/transmitting apparatus which alternately performs frequency synthesis according to a fixed synthetic ratio, in response to two reference signals with different frequencies, to generate the first signal and the second signal.
In the receiving/transmitting apparatus as described above, switching frequencies of the first signal used for generating an emission wave or corresponding to the emission wave and the second signal used for receiving a reception wave is realized as updating an oscillating frequency of means for generating the reference signals.
The above objects are also achieved by a receiving/transmitting apparatus which alternately performs frequency synthesis according to two different synthetic ratios, in response to two reference signals with different frequencies, to generate the first signal and the second signal.
In the receiving/transmitting apparatus as described above, the frequency of the first signal used for generating an emission wave or corresponding to the emission wave and the frequency of the second signal used for receiving a reception wave are determined according to the combination of an oscillating frequency of means for generating the two reference signals, and the aforesaid synthetic ratios.
The above objects are also achieved by a receiving/transmitting apparatus which generates the first signal and the second signal by reading a sequence of instantaneous values of signals individually corresponding to the first signal and the second signal, during periods in which the first signal and the second signal are to be generated respectively. The sequence of the instantaneous values is stored in the storage areas of the storage section corresponding to the respective periods.
In the receiving/transmitting apparatus as described above, the first signal and the second signal are generated as the sequence of the instantaneous values which are stored in the storage section in advance and read so that the first and second signals are constantly obtainable compared with a case where the first and second signals are generated by an oscillating circuit which intermittently oscillates the first signal and/or the second signal or an oscillating circuit whose oscillating frequency is alternately switched.
The above objects are also achieved by a receiving/transmitting apparatus which generates the first signal and the second signal in conformity with direct frequency synthesis which does not include a frequency-mixing process.
In the receiving/transmitting apparatus as described above, the first signal and the second signal are generated alternately without any means for constantly or continuously generating a local-frequency signal being provided.
The above objects are also achieved by a receiving/transmitting apparatus which generates the first signal and the second signal in conformity with direct frequency synthesis which includes a frequency-mixing process and in which a leak in a local-frequency signal used for the frequency-mixing is suppressed to such an extent that the components of a reception wave can be separated with desirable precision.
In the receiving/transmitting apparatus as described above, even with means for constantly or continuously generating the local-frequency signal, the first signal and the second signal are alternately generated without any means provided for setting loose coupling or shielding coupling with the means.
The above objects are also achieved by a receiving/transmitting apparatus which generates the first signal and the second signal, in conformity with indirect frequency synthesis or frequency synthesis including a process of the indirect frequency synthesis. The indirect frequency has responsiveness such that the phase of the second signal is fixed with a desirable precision at the starting point of a period during which a reception wave to be separated at its every phase relative to the first signal or the second signal, arrives.
In the receiving/transmitting apparatus as described above, the first signal and the second signal are generated by a low-priced, general-purpose phase lock oscillator as long as the indirect frequency synthesis is achieved in a short lock-up time where the above-described condition can be satisfied.
The above objects are also achieved by a receiving/transmitting apparatus where the components of each reception wave separated at its every phase relative to the first signal or the second signal are integrated in parallel at its every phase.
In the receiving/transmitting apparatus as described above, the integrating processing is performed for each group of components of the reception waves which have the same phase and are received from a target as responses to emission waves intermittently transmitted at the same phase level every time.
The above objects are also achieved by a radar equipment along with the above receiving/transmitting apparatus. The radar equipment performs signal processing associated with measurement of all or a part of the characteristic of a medium interposed between the radar equipment and its target, a relative distance and a relative position to the target, and a relative speed and a size of the target, based on the components of a reception wave which is separated at its every phase relative to an emission wave by the receiving/transmitting apparatus.
In the radar equipment as described above, the above signal processing is performed for each group of components of the reception wave having the same phase, based on various digital signal processing such as integration, correlation, and others.
The above objects are also achieved by a radar equipment which identifies a target based on the measurement result.
In the radar equipment as described above, the measurement is performed with efficiency and high reliability even when a reception wave is very weak, as long as the characteristic of a propagation path, which is interposed between the radar equipment and a target, for an emission wave and the reception wave, a time required for the target to respond, and the characteristic of the target do not vary.
The above objects are also achieved by a radar equipment along with the above receiving/transmitting apparatus. The radar equipment performs signal processing associated with measurement of all or a part of the characteristic, shape, size, and material of medium through which an emission wave and a reception wave propagate, based on the components of the reception wave which is separated at its every phase relative to the emission wave by the receiving/transmitting apparatus.
In the radar equipment as described above, its target is identified by performing processing such as integration, correlation, and others on the phase discriminated with high precision so that reliability and precision in target identification are highly maintained.